FAVEum Framework Architecture for Virtual Environments Applied to Urban Modelling J. O. Erdal, T. Langeland, D. Patel, I. K. Eliassen Christian Michelsen Research (CMR) (www.cmr.no) P. O. Box 6031 Postterminalen, N-5892 Bergen, Norway {jone, tor, daniel, ingekr}@cmr.no KEY WORDS: Virtual environment, 3D user interaction, rapid prototyping, configurable framework, authoring system, urban modelling, new paradigms for 3D GIS, innovative visualization techniques ABSTRACT: FAVE (Framework Architecture for Virtual Environments) is a generic software framework for developing VR applications. It contains a toolkit of user interface widgets, navigation techniques, interaction features and optimised visualisation algorithms. Non- programmers can specify application behaviour. Applications developed in the framework can be used on different platforms, from immersive stereographic VR-environments down to desktop computers. In this paper we present development and tests of a 3D urban modelling application based on FAVE. We have selected a few functionalities important to urban modelling relevant to user demands, such as modular scaling, silhouette analysis, design comparison, as well as safety and risk analysis. In addition, we present three functionality examples in our application prototype (FAVEum) based on the rapid prototyping qualities within FAVE. The chosen functionalities have been tested using a simple 3D model of a part of Bergen, Norway. 1. INTRODUCTION We present a highly configurable, rapid prototyping framework for immersive virtual environments, FAVE (Patel, 2003). The Immersive Virtual Reality (VR) is an aid to mastering spatial framework is object oriented, event driven and has been complexities, by facilitating improved understanding of 3D data designed with collaboration over networks in mind. It consists and offering new modes of interdisciplinary collaboration. of several abstraction layers and application behaviour is Immersive VR has gained usage within a range of application separated from graphical data and is specified using XML. This areas, e.g. design, medicine, oil, and gas exploration, as well as enables development by non-programmers and facilitates production. The authors of this paper are expecting an comparisons of different user interaction strategies. increasing use of immersive VR also within urban planning and modelling. Issues regarding 3D user interaction have been investigated, including an efficient, context-sensitive, hierarchical extension to the command and control cube. The framework has been used to prototype an urban modelling application, FAVEum (Figure 1). One important motivation for developing a system facilitating easy configuration of user interface and application behaviour is that we are interested in comparing user interaction methodologies for VR in general. Challenges related to developing efficient user interfaces for virtual environments (VE) delay the utilization of the full potential of the VR technology. User interface design is held to be one of the great challenges within computer science (Brooks, 2003). The FAVE framework facilitates easy and rapid comparisons of different Figure 1. A model of the Bergen area with buildings at Kron- user interaction strategies. In the urban modelling prototype we stad (near) and downtown (far). To the right is a have used these capabilities to experiment with different user menu for importing buildings. Also shown is a interface elements. spline with control points representing an editable flight path The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 34, Part XXX 2. RELATED WORK System control is defined (Bowman, 2001) as the task of VR frameworks cover many different domains. Frameworks changing the interaction mode or the state of the system by like CAVELib (CAVELib) and VR Juggler (Bierbaum, 2001) issuing commands. These commands are issued in our system offer support for basic VR functionalities, such as stereoscopic by means of interacting with controllers. The Controller class is viewing and device sampling. The Quanta (previously used to implement simple widgets, such as buttons, sliders and CavernSoft) framework (He, 2003) is an API for network menus, as well as more complicated tools, e.g. for managing communication, such an API is necessary for extending a single editable flight paths. user VR application to a collaborative application. Many higher-level VR frameworks use these or similar building blocks accompanied by specialized graphics libraries or com- mercial ones like OpenGL Performer (OpenGL Performer). In addition some frameworks come with a scripting environment, making them more flexible and configurable. Frameworks supporting scripting often also support the dataflow approach seen in SGI’s Open Inventor (Open Inventor) and in VRML 2.0 (Carey, 1997). In Inventor and VRML 2.0 the flow of data between virtual world entities is established by creating channels or connections between the different entities’ attribute values. Avango (Springer) is an example of a framework that supports scripting. 3D urban models can cover a wide range of topics, and the focus areas are naturally depending, both in size and scope, on Figure 3. Main menu as a menu bar the role of the users – the general public (car navigation (SONY, 2005), and web based information (NMM)), urban The distinction between widgets and tools is not always as well planning commissions, urban planners, site developers (urban defined in virtual environments as in traditional desktop WIMP design guidelines (Mak, 2004)), large scale project proposals environments. Some controllers in the scene can be multi- and presentations (Olympic Games & Urban Development of functional and act as both widgets and tools. One difference, Beijing, CrystalCG), emergency operators (safety analysis and though, is that the controllers acting as widgets tend to provide training (Jafari, 2003)), to mention a few. more elementary behaviour and will probably be reused across different application domains, whereas the more advanced tools Observing different discipline-specific approaches, we note that are generally more bound to specific application domains. usage of 3D models are well integrated with visual assessment methods widely applied within landscape architecture (Lange, 1999, Ervin 2001), in addition to the more database-oriented and multi-applicable approaches often found within geomatics (Zlatanova, 2000). Within computer-aided architectural design, references are also rich (CumniCAD), showing a developing terminology (Martens, 2001) and a globally well organized professional field (Architectural Computing Organisation). 3. INTERACTION TECHNIQUES The toolbox of controllers in FAVE implements a wide range of interaction techniques. Interaction techniques are typically Figure 4. Controller widgets, menu showing two buttons and divided into four groups: navigation, selection, manipulation, tool-tip text and system control. We have implemented controllers that can be used as a widget library. Figures 2, 3 and 4 show applicable usages of these widgets. Each instantiated widget will have a tag in the XML file. The central widgets in this library are buttons and toggle- buttons for performing discrete commands (the icons in Figures 2, 3 are buttons, and Figure 4 toggle buttons), sliders for specifying step-wise values (Figure 8), text windows for showing lines of text and menu bars (Figure 3) and C3 cuboids (Figure 2) as two different ways of presenting a hierarchy of commands to select among. The C3 cuboid was inspired by ideas from the Command and Control Cube (Grosjean, 2002). It is a powerful metaphor for structuring and presenting collections of commands, possibly in hierarchies, using very little screen area and having quick and precise navigability. We have called the widget a C3 cuboid Figure 2. Main menu as C3 due to its shape; its edges are drawn as lines. The cuboid is a The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 34, Part XXX 3D matrix consisting of equally sized smaller cubes, each The main menu is configured in two different versions for containing a geometry representing a controller. comparison reasons. One version is a C3 cuboid, the other is a menu bar. Both versions are accessible by selecting semi- transparent icons located in the upper left part of the screen. 4. FAVE APPLIED TO URBAN MODELLING These icons are fixed in device space coordinates, making them always close to the user. Moreover, by being semitransparent For the purpose of evaluation and gaining experience the FAVE and not in the central view area they don’t disturb the sense of framework has been used to prototype an urban modelling being immersed in the virtual environment. The C3 main menu application. The application runs on Linux PCs and on SGI is also a context menu attached to the ground geometry. This Onyx graphics computers, and can easily be ported to any other means that the main menu also can be reached by selecting the platform with support for the libraries CAVELib and OpenGL ground and right-clicking. Performer. The application makes use of two different modes, a desktop mode (applying a mouse and a keyboard), and an The context sensitive hierarchical C3 menu system has proven immersive stereo mode with head tracking and a 3D mouse to be useful and effective. It is conveniently placed right in with three buttons and a joystick. front of the user when activated, and is otherwise